try this method and solve your doubts.
Connection connection = DriverManager.getConnection(url, username, password);
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery("SELECT col_blob FROM mysql_all_table");
if (rs.next()) {
Blob blob = rs.getBlob("col_blob");
long blobLength = blob.length();
int pos = 1; // position is 1-based
int len = 10;
byte[] bytes = blob.getBytes(pos, len);
InputStream is = blob.getBinaryStream();
int b = is.read();
another example tojust goto this link
listen to me, if you had any doubt you should must give me comments.